For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane comprises a polymer ion exchange membrane. The membrane electrode assembly is sandwiched between separators. In use, generally, a predetermined number of fuel cells are stacked together to form a fuel cell stack, which is mounted in a vehicle.
In general, several tens to hundreds of fuel cells are stacked together to form the fuel cell stack. In this regard, it is required to accurately position each of the fuel cells themselves relative to each other. For example, a fuel cell stack of this type is disclosed in Japanese Laid-Open Patent Publication No. 2009-283469.
As shown in FIG. 16, the fuel cell stack is formed by stacking a plurality of fuel cell units 1 together. Each of the fuel cell units 1 includes first and second membrane electrode assemblies 2a, 2b, and first, second, and third separators 3a, 3b, and 3c. The fuel cell units 1 are positioned together by a positioning mechanism 4. The positioning mechanism 4 includes positioning members 5. Each of the positioning members 5 is formed integrally with an end of the second separator 3b, and both ends of the positioning members 5 are engaged with the first separator 3a and the third separator 3c. 